Communication control apparatus for determining data transmission timing with node type and a state variable

ABSTRACT

A communication control apparatus, mounted on each node of a telecommunications system, receives node type information selected by a neighboring node, and transmits node type information selected by the own node and node type information of another node. The apparatus receives the state variable signal of the neighboring node reflecting a phase representing another node&#39;s data transmission timing, and transmits a state variable signal representing the own node&#39;s data transmission timing. Subsequently, the apparatus selects the own node&#39;s node type in accordance with another node&#39;s type information received. The apparatus then varies, based on the own node&#39;s node type information selected, another node&#39;s node type information and the neighboring node&#39;s state variable signal, the state of the own node&#39;s phase in accordance with a time evolution rule based on a phase response function and a synchronization alliance function for thereby determining the own node&#39;s data transmission timing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication control apparatus for atelecommunications system, and more particularly to a communicationcontrol apparatus applicable to a telecommunications system, such as asensor network, a local area network (LAN), which is formed by aplurality of network node devices spatially distributed or carried onmobile bodies to transmit data therebetween, for obviating a collisionbetween transmitted data ascribable to interference of electromagneticwaves or similar cause.

2. Description of the Prior Art

For allowing a plurality of spatially distributed nodes to transmit andreceive data therebetween without any collision, available are a timedivision multiple access (TDMA) system and a carrier sense multipleaccess (CSMA) system such as a CSMA/CA (Carrier Sense Multiple Accesswith Collision Avoidance) system and a CSMA/CD (Carrier Sense MultipleAccess with Collision Detection) system, as taught in Y. Matsushita etal., “Wireless LAN Architecture”, pp. 47, 53-59 and 69, Kyoritsu ShuppanCo., Ltd., Tokyo, Japan, 1996.

One of the problems with the TDMA system is that, when a central ormanagement node expected to allot time slots fails, the entiretelecommunications system goes down. In light of this, there have beenproposed various methods of obviating a collision between transmitteddata by causing the individual nodes to mutually adjust the allotment oftime slots in a distributed coordination or self-organizing fashionwithout resorting to a central control server. For such mutualadjustment, each node transmits and receives periodic impulse signals toand from its neighboring nodes to interact with them.

More specifically, each node is adapted for using expressions modelingnonlinear oscillation to take account of the timing at which anothernode transmits an impulse signal to thereby adjust its own timing forthe transmission of an impulse signal. With this adjustment scheme, theindividual nodes execute mutual adjustment such that the transmissiontiming of an impulse signal from the own node is apart as far from thetransmission timing of an impulse signal from another node as possible,implementing the allotment of time slots in a distributed coordinationor autonomous fashion.

Further, when nodes are spatially distributed in a planer lattice ormatrix arrangement, there may be implemented an optimum time-divisiontransmission pattern in which only neighboring nodes, lying in a firstrange, mutually share a time slot, as also proposed in the past. Morespecifically, the transmission timings of nodes, lying in a third rangeand held in a particular positional relation free from collisions, aresynchronized to each other, so that neighboring nodes, lying in thefirst range, can mutually share a single period with each other.Consequently, a time slot which each node is acquirable can bemaximized. In this sense, the optimum dime-division transmission andhence ideal, high-level communication efficiency is achievable.

However, the above-stated communication control system, implementing theoptimum time-division communication by the individual nodes, isapplicable to a telecommunications system or network in which aplurality of nodes are spatially distributed in a lattice configuration,but not to other types of telecommunications systems or networks notusing the lattice configuration.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a communicationcontrol apparatus for a telecommunications system, and a methodtherefor, capable of implementing the optimum time-divisioncommunication and therefore enhancing communication efficiency even in asystem in which nodes are not arranged in a lattice pattern.

A communication control apparatus of the present invention is mounted oneach of a plurality of nodes constituting a telecommunications system.The communication control apparatus includes a node type informationtransmitter/receiver for receiving node type information selected by aneighboring node and transmitting node type information selected by theown node and node type information of another node. A state variablesignal transmitter/receiver receives the state variable signal of theneighboring node reflecting a phase representative of the timing of datatransmission from the neighboring node and transmits a state variablesignal representative of the timing of data transmission from the ownnode. A node type selector selects the node type of the own node inaccordance with node type information of the other node received via thenode type information transmitter/receiver. A transmission timingcalculator varies, based on the node type information of the own nodeselected by the node type selector and the node type information of theother node as well as the state variable signal of the neighboring node,the state of the phase of the own node in accordance with a timeevolution rule based on a phase response function and a synchronizationalliance function for thereby determining a data transmission timing ofthe own node.

A node loaded with the above communication control apparatus, acommunication system including a plurality of such nodes and acommunication control method applied to each node are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become moreapparent from consideration of the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a schematic block diagram showing the general construction ofa first embodiment of the communication control apparatus in accordancewith the present invention;

FIG. 2 is a schematic block diagram showing a specific configuration ofthe node included in the illustrative embodiment shown in FIG. 1;

FIGS. 3A, 3B and 3C demonstrate a specific condition in which two nodesare tuned to each other;

FIGS. 4A, 4B and 4C demonstrate another specific condition in whichthree nodes are tuned to each other;

FIG. 5 shows a specific structure of type information included in theillustrative embodiment;

FIG. 6 is a flowchart useful for understanding a specific type selectionprocedure executed by a node type selector included in the illustrativeembodiment;

FIG. 7 is a schematic block diagram showing a specific configuration ofa transmission timing calculator included in the illustrativeembodiment;

FIG. 8 is a schematic block diagram showing a specific configuration ofa phase synchronization alliance circuit included in the illustrativeembodiment;

FIG. 9 is a schematic block diagram showing another specificconfiguration of the transmission timing calculator representative of asecond embodiment of the present invention;

FIG. 10 is a flowchart useful for understanding a specific typeselection procedure executed by a node type selector included in thesecond embodiment;

FIG. 11 is a schematic block diagram showing a fourth embodiment of thenode in accordance with the present invention;

FIG. 12 is a flowchart useful for understanding a specificnumber-of-types determining operation unique to the fourth embodiment;

FIG. 13 is a flowchart useful for understanding specific numberincreasing processing included in a number-of-types determiningoperation representative of a fifth embodiment of the present invention;and

FIG. 14 is a flowchart useful for understanding specific numberdecreasing processing also included in the number-of-types determiningoperation of the fifth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 and 2 of the drawings, a first embodiment ofthe communication control apparatus for a telecommunications networksystem in accordance with the present invention is applied to a sensornetwork made up of a plurality of nodes by way of example. Specifically,FIG. 1 shows the general construction of the communication controlapparatus while FIG. 2 shows a specific configuration of a node includedin the illustrative embodiment. Generally, as seen from FIG. 1, theillustrative embodiment is capable of selectively executing twodifferent procedures, i.e. one that executes consecutive steps enclosedby a dotted rectangle 41 as preprocessing and then performs transmissiontiming calculation after the convergence of node type selection, and theother that executes node type selection and transmission timingcalculation in parallel, as will be described specifically later.

As shown in FIG. 2, the node, generally 10, includes an impulse signalreceiver 11, a transmission timing calculator 12, an impulse signaltransmitter 13, a tuning decision circuit 14, a datatransmitter/receiver 15, a sensor 16, a node type selector 17, a nodetype signal receiver 18 and a node type signal transmitter 19, which areinterconnected as illustrated. The impulse signal receiver 11,transmission timing calculator 12, impulse signal transmitter 13, tuningdecision circuit 14 and node type selector 17 constitute thecommunication control apparatus.

The impulse signal receiver 11 is adapted to receive an input impulsesignal Sin11, transmitted from a neighboring node, e.g. a node lying ina range over which an electromagnetic wave transmitted from the node 10can propagate. The impulse signal, transmitted and received as a timingsignal, has a Gaussian distribution or similar impulse waveformdistribution. The impulse signal may contain destination address, e.g.address information representative of the spatial position of the ownnode, if desired. The impulse signal receiver 11 is adapted to output areceived impulse signal Spr11, resultant from shaping the waveform ofthe input impulse signal Sin11 or regenerating itself.

The transmission timing calculator 12 is adapted to be responsive tonode type information 43 selected by the node type selector 17 andreceived impulse signal Spr11 to generate a phase signal Spr12, whichdetermines or defines the transmission timing of the node 10, as will bedescribed more specifically later. It should be noted that thetransmission timing calculator 12 outputs the phase signal Spr12 evenwhen the received impulse signal Spr11 is absent.

Assuming that the phase signal Spr12 of a node i has a value of θ_(i)(t)at a time t, then the transmission timing calculator 12 varies the phasesignal Spr12 (=θ_(i)(t)) in nonlinear oscillation rhythm in response tothe received impulse signal Spr11, as will be described later morespecifically. The variation of the phase signal realizes a nonlinearcharacteristic that causes nearby nodes to tend to become opposite inphase (inversion of an oscillation phase) or become different in phasefrom each other. In other words, in order to prevent, e.g. thetransmission timings of output impulse signals Sout11 transmitted fromthe neighboring nodes from colliding with each other, the illustrativeembodiment uses such a nonlinear characteristic for avoiding collisions,i.e. establishes a suitable time relation or time lag.

The functional principle of the transmission timing calculator 12 willbe described more specifically with reference to FIGS. 3A through 3C and4A through 4C. It is to be noted that the function of the impulse signaltransmitter 13 also relates to state transitions shown in FIGS. 3Athrough 4C. Paying attention to a given node, FIGS. 3A through 4Cdemonstrate a relation between the given node or node of interest i anda neighboring node or nodes j, i.e. how a phase relation between thenonlinear oscillation rhythms of the nodes i and j varies with theelapse of time.

FIGS. 3A, 3B and 3C show a specific case wherein a node of interest orown node i and a single node j adjoining it exist together. In FIGS. 3A,3B and 3C, two material points, rotating on a circle 45, arerespectively representative of the nonlinear oscillation rhythms of thenode of interest i and the neighboring node j. The angles θ_(i) andθ_(j) of the material points i and j, respectively, on the circle 41 arerepresentative of the instantaneous values of phase signals. Thecircular movements of the material points i and j are projected onto theordinate or the abscissa to represent the respective nonlinearoscillation rhythms. The two material points i and j tend to becomeopposite in phase to each other in accordance with the operation basedon an expression (5) to be described specifically later. As a result,even if the phases of the two material points i and j are close to eachother, as shown in FIG. 3A, the state varies as the time elapses via atransition state shown in FIG. 3B to a stable state shown in FIG. 3C inwhich the phase difference between the two points i and j issubstantially equal to pi, n.

The two material points i and j each rotate at particular primaryangular velocity equal to the respective specific angular oscillationfrequency parameter ω. The primary angular velocity corresponds to thebasic velocity at which a material point varies its state. When the twonodes become interactive in response to impulse signals transmittedtherebetween, the two points i and j vary the respective angularvelocities ahead or behind so as to ultimately establish the stablestate at which the appropriate relation is maintained. This operationmay be considered to indicate that the two points i and j repel eachother while rotating to establish the stable phase relation. In thestable state, FIG. 3C, if each of the two nodes i and j is in itspredetermined phase, e.g. zero, to transmit the output impulse signalSout11, then the transmission timings of both nodes establish theadequate timing relation with each other.

FIGS. 4A, 4B and 4C show another specific case wherein the own node iand two neighboring nodes j1 and j2 exist together. In this case, too,the material points i, j1 and j2 repel each other while, in rotation,establishing the stable phase relation with respect to time. This isalso true when three or more nodes neighbor the node of interest i.

The stable phase relation or stable state thus established is, innature, remarkably adaptive to a change in the number of neighboringnodes, i.e. remarkably flexible. For example, assume that when a singlenode j1 neighbors the node of interest i in a stable phase relation orstable state, another neighboring node j2 is added. Then, although thestable state is once disturbed, a new stable state is again establishedbetween the node of interest i and two neighboring nodes j1 and j2 via atransitional or transient state. This is also true when either one ofthe neighboring nodes j1 and j2 disappears or fails due to an error orsimilar cause occurring therein.

In the illustrative embodiment, the transmission timing calculator 12 isadapted for using the expression (5) to be described later specificallyto establish a mutual, stable phase relation. The transmission timingcalculator 12 delivers the phase signal Spr12 (=θ_(i)(t)) calculated tothe impulse signal transmitter 13, tuning decision circuit 14 and datatransmitter/receiver 15.

The impulse signal transmitter 13 is adapted to transmit an outputimpulse signal Sout11 in response to the phase signal Spr12, i.e. whenthe phase signal Spr12 reaches a predetermined phase a (0≦α<2π). Thepredetermined phase α should preferably be uniform in the entiretelecommunications system and will be assumed to be zero hereinafter. Inthe state shown in FIG. 3C, because the phase signals of the nodes i andj differ in phase from each other by n in the stable state, thetransmission timings of output impulse signals from the node i and j areshifted from each other by π despite that α is uniform in the entiresystem.

The tuning decision circuit 14 is adapted to determine whether mutualadjustment or tuning executed between the own node and one or moreneighboring nodes as to the transmission timing of the output impulsesignal Sout11 is in the transition state shown in FIG. 3B or 4B or inthe stable state shown in FIG. 3C or 4C. More specifically, the tuningdecision circuit 14 monitors the generation timing of the receivedimpulse signal Spr11, which corresponds to the output impulse signalSout11 of another node, and the generation timing of the output impulsesignal Sout11. The decision circuit 14 determines that the mutualadjustment mentioned above is in the stable state if the time lagbetween the transmission timings of the nodes, which transmit andreceive impulse signals with each other, is stable with respect to time.In the illustrative embodiment, in order to allow the tuning decisioncircuit 14 to grasp the generation timing of the output impulse signalSout11 to be transmitted from the own node, the circuit 14 is connectedto receive the phase signal Spr12 instead of the output impulse signalSout11.

To make the above decision on tuning, the tuning timing calculator 14may execute the following specific sequence of steps. The tuningdecision circuit 14 monitors, over a single period of the phase signalSpr12, the value β of the phase signal Spr12 occurring at the outputtime at which the received impulse signal Spr11 is output. Assume thatthe values β of the phase signal θ_(i)(t) thus monitored are β₁, β₂, . .. , β_(N) (0<β₁<β₂< . . . β_(N)<2π). The tuning decision circuit 14 thencalculates, based on the monitored values β, differences between nearbyvalues, i.e. phase differencesΔ₁=β₁,Δ₂=β₂−β₁, . . . , Δ_(N)=β_(N)−β_((N−1)).

The tuning decision circuit 14 executes the steps stated above everyperiod of the phase signal Spr12 to thereby produce variations ordifferences, γ₁=Δ₁(τ+1)−Δ₁(τ), γ₂=Δ₂(τ+1)−Δ₂(τ), . . . ,γ_(N)=Δ_(N)(τ+1)−Δ_(N)(τ) between the phases in the consecutive periodswhere τ denotes a given phase of the phase signal Spr12 while τ+1denotes a period immediately following the period of the phase signalSpr12. Thereafter, the tuning decision circuit 14 determines that thetuning is in the stable state when the variations γ all are smaller thana small parameter or threshold value ε, i.e. when there holds relationsof γ₁<ε, ε₂<ε, . . . , γ_(N)<ε. Alternatively, the tuning decisioncircuit 14 may be adapted for determining that the tuning is in thestable state when the relations γ₁<ε, γ₂<ε, . . . , γ_(N)<ε arecontinuously satisfied over a consecutive plurality (M) of periods, inwhich case the degree of the stable state increases with an increase inthe number M of consecutive periods. Further, the tuning decisioncircuit 14 may be adapted to make a decision on the stable state inresponse to part of or some kind of received impulse signals Spr11.

The tuning decision circuit 14 feeds, every period of the phase signalSpr12, the data transmitter/receiver 15 with a tuning decision signalSpr13 representative of the result of a decision and a slot signalSpr14, which is the minimum value β₁ of the value β of the phase signalSpr12 appearing at the time when the received impulse signal Spr11 isgenerated. Why the minimum value β₁ is output as a slot signal Spr14 isrelated to the condition of α=0, so that the value β applied to the slotsignal Spr14 varies in accordance with the value α selected.

The node 10 serves as selectively relaying data received from anothernode or transmitting data originally generated therein. The sensor 16 isprovided, as an example of the source of data originating in the node10, to sense or catch information Sin13 on the intensity of sound oroscillation, the density of a chemical substance, temperature or similarphysical or chemical environment to feed the resulting sensedinformation Spr15 to the data transmitter/receiver 15. As an example ofdata to be relayed by the node 10, a data signal transmitted from aneighboring node, corresponding to an output data signal Sout12described later, is input to the data transmitter/receiver 15 of thenode 10 as an input data signal Sin12.

The data transmitter/receiver 15 is further adapted to transmit thesensed data Spr15 and/or the input data signal Sin12 to another node inthe form of output data signal Sout12. More specifically, the datatransmitter/receiver 15 executes such transmission in a time slot, whichis different from a conventional, fixed time interval allotted by, e.g.a system, when the tuning decision signal Spr13 is representative of astable state. The transmitter/receiver 14 does not execute suchtransmission when the signal Spr13 is representative of a transitionalstate. The output data signal Sout12 has its transmission frequencywhich may lie in the same frequency band as the output impulse signalSout11.

In the illustrative embodiment, the term “time slot” mentioned aboverefers to a time interval in which the phase θ_(i)(t) of the phasesignal Spr12 lies in the range of δ₁≦θ_(i)(t)≦β₁−δ₂. The start point ofthe time slot at which the phase signal is assumed to have the abovevalue δ₁ is a time at which the transmission of output impulse signalSout11 ends. On the other hand, the end point of the time slot at whichthe phase signal is assumed to have the value β₁−δ₂ is a time precedingthe timing of the first impulse signal Spr11 in every period of thephase signal Spr12 by some offset δ₂. The values δ₁ and δ₂ arerepresentative of a phase width corresponding to a minute or shortperiod of time for ensuring that impulse and data signals do not exit atthe same time regardless of the signals having been sent out from theown node or other nodes.

The values δ₁ and δ₂ are determined by, e.g. experiments incircumstances in which the node 10 is located. For example, in thestable state shown in FIG. 3C, the node i starts transmitting the outputimpulse signal Sout11 when the phase θ_(i) is zero, ends thetransmission of the output impulse signal Sout11 before the phase θ_(i)reaches δ₁, starts sending out the output data signal Sout12 when thephase θ_(i) is equal to δ₁, ends the transmission of the data signalSout12 when the phase θ_(i) reaches a value β₁−δ₂ where β₁ is nearlyequal to π, and then keeps stopping the transmission of the impulsesignal Sout11 and data signal Sout12 until the phase θ_(i) again becomeszero. Although the other node j operates in the same manner as the nodei on the basis of a phase θ_(j), the transmitting operations of the twonodes i and j do not coincide with each other because the phases θ_(i)and θ_(j) are shifted from each other by about π. This is also true witha case wherein the number of nodes is three or more.

The node type signal receiver 18 and node type signal transmitter 19will be described in detail hereinafter. The node type signal receiver18 is adapted to receive a node type signal 47 sent out from anothernode and feed the input node type signal 49 to the node type selector17. Each node stores type information contained in the node type signals47 sent out by broadcast from neighboring nodes and received by the nodetype signal receiver 18. The node type selector 17, which will bedescribed specifically later, selects the type of the own node inaccordance with the type information stored in the node to develop nodetype information 51.

The node type transmitter 19 is adapted to transmit by broadcast, whenhaving received the type information 51 from the node type selector 17,a node type signal 53 representative of the type information. The nodetype transmitter 19 may be implemented by the conventional CSMA/CAsystem. The node type signal mentioned above is a signal representativeof type information selected by each node included in thetelecommunications system.

FIG. 5 shows a specific structure of the node type information 51included in the node type signal 53 transmitted and received betweennodes. Assume that the node type signal 53 is capable of propagatingover a distance of r. Then, in FIG. 5, nodes lying in a first rangeadjacent to a node i refer to nodes present in the range of distance rfrom the node i, i.e. nodes which the node type signal can directlyreach by a single hop. In the illustrative embodiment, the distance r isassumed to be identical in the entire system. Nodes lying in a k-thrange (k=1, 2, 3, . . . ) adjacent to the node i refer to nodes whichthe node type signal can reach by k hops from the node i, or k hopsapart from the node i, by being relayed by other nodes.

Further, in FIG. 5, O_(k) (k=1, 2, 3, . . . ) denotes a node set lyingin the k-th range except for a (k−1)-th range adjacent to the node i.Also, “i” of O^(i) denotes a node number; O^(i) will not be usedhereinafter because of limitations on denotation. Moreover, τ(*) denotesa type or a type set. More specifically, a node i is capable ofdetermining, based on type information received from a neighboring node,the number of hops between the node i and the range in which theneighboring node lies and type information selected by the neighboringnode. While the maximum value of k is shown as being “3” in FIG. 5, itis generally open to choice.

Referring again to FIG. 2, the node type signal transmitter 19transmits, by broadcast, a node type signal 53 including not only typeinformation 51 selected by the node 10 but also type information 49received from neighboring nodes shown in FIG. 5.

It should be noted that the type information included in the node typesignal 53 do not have to include all type information 49 received fromneighboring nodes. For example, when type information of neighboringnodes stored in the node i are τ(O₁), τ(O₂) and τ(O₃), FIG. 5, only thenode type information τ(O₁) and τ(O₂) may be sent out with the typeinformation τ(O₃) being omitted. In such a case, the node type signaltransmitter 19 transmits the node type signal 53 carrying the typeinformation 49 of neighboring nodes two hops apart from the node itogether with the type information 51 selected by the node i. It followsthat when the node i receives a node type signal 47 from any one of theneighboring nodes a single step apart from the node i, the node i canobtain even the type information of the neighboring nodes three hopsapart from the node i. This, however, would not be practicable withouttransmitting the node type signal in three hops.

The node type selector 17 is adapted to select the type of the own node10 in accordance with the information 49 of neighboring nodes receivedand stored by the node type signal receiver 18. Also, the node typeselector 17 delivers the type information 51 and 43 of the own node 10to the node type signal transmitter 19 and transmission timingcalculator 12, respectively. The node type selector 17 repeats theselection of the type of the own node every preselected period. Suchrepeated selection of the type does not have to be synchronized to othernodes, but may generally be executed asynchronously to other nodes.

How the node type selector 17 selects a node type will be describedspecifically hereinafter. In the following description, the typeinformation of neighboring nodes stored in each node is assumed to beτ(O₁), τ(O₂), . . . , τ(O_(n)) while the kinds of node types arerepresented by 1, 2, . . . , Ntyp, where Ntyp is a natural number.

Further, a node set A_(n) is assumed to be representative of nodes nhops apart from the node i and selecting a type σ, where σε{1, 2, . . ., Ntyp}. It is to be noted that the expression A^(i) is omittedhereinafter because of limitations on denotation. The number of elementsincluded in the node set A_(n), i.e. the total number of nodes n hopsapart from the node i and selecting the type σ, where σε{1, 2, . . . ,Ntyp}, is assumed to be |A_(n)(σ)|; again A^(i) is omitted because oflimitations on denotation. In addition, the total number of nodes n hopsapart from the node i is assumed to be |N_(n)|; N^(i) is omitted for thesame reason as A^(i).

Assume that the node i is selecting a type α, i.e, τ(i) is α. Then, thenode type selector 17 determines the adaptability F_(i)(σ) of the nodeon the basis of the total number of nodes |An (σ)| included in the nodeset n hops apart from the node i and selecting the same type σ as thenode i. The adaptability F_(i)(σ) is expressed as: $\begin{matrix}\begin{matrix}{{F_{i}(\sigma)} = {\exp\left( {{- \eta} \cdot \frac{{A_{n}^{i}(\sigma)}}{N_{n}^{i}}} \right)}} & {\eta > 0}\end{matrix} & (1)\end{matrix}$where the element |A_(n) ^(i)(σ)| denotes a node set n hops apart fromthe node i and selecting a type σ (τε{1, 2, . . . , Ntyp}), |A_(n)^(i)(σ)| denotes the number of elements constituting a node set A_(n),i.e. the total number of nodes n hops apart from the node i andselecting the type σ, |N_(n) ^(i)| denotes the total number of nodes nhops apart from the node i, and η denotes a constant experimentallydetermined.

The adaptability F_(i)(σ), which lies in the range of 0<F_(i)(σ)≦1,decreases with an increase in the number of nodes selecting the sametype σ as the node i, i.e. with an increase in the number of overlappingselections. It increases with a decrease in the number of such nodes.The adaptability F_(i)(σ) is “1” only when no nodes are selecting thesame type σ as the node i. In this sense, the adaptability F_(i)(σ) is ascale for estimating the degree of selection of the same type by thenode i and neighboring nodes, i.e. overlapping selections.

Subsequently, the node type selector 17 determines, based on theadaptability F_(i)(σ) thus determined, the easiness f_(i)(ρ) ofselection of each type ρ, where ρε{1, 2, . . . , Ntyp}, by the node i.The easiness f_(i)(ρ) is produced by:f _(i)(ρ)=exp(−ζ·|A _(n) ^(i)(ρ)|)  (2)whereζ=α·F _(i)(σ)+b a>0,b≧0  (3)where a and b are constants experimentally determined.

The easiness f_(i)(σ) of selection of the type σ is an evaluation scalecharacterized in that, when the adaptability F_(i)(σ) is high, typesother than one whose A_(n)(σ) is zero are difficult to be selectedwhile, when the adaptability F_(i)(σ) is low, even types with relativelysmall values A_(n)(σ) other than zero are easily selectable. Byproviding the easiness f_(i)(σ) of the selection of a type with theabove characteristic, it is possible to prevent the type selection fromfailing to converge in some nodes.

The node type selector 17 then produces, based on the easiness f_(i)(σ)of type selection, a probability P_(i)(ρ) that the node i selects eachtype p. The probability P_(i)(ρ) is produced by: $\begin{matrix}{{P_{i}(\rho)} = \frac{f_{i}(\rho)}{\sum\limits_{k = 1}^{Ntyp}{f_{i}(k)}}} & (4)\end{matrix}$

In the node i, the node type selector 17 calculates the probability ofselection P_(i)(ρ) of each type ρ, where ρε{1, 2, . . . , Ntyp}, by useof the expressions (1) through (4) and then selects a type in accordancewith the calculated probability P_(i)(ρ). More specifically, when thenode i is selecting a type σ, the node type selector 17 calculates aprobability P_(i)(ρ) based on the easiness of selection f_(i)(σ) of eachtype, which is dependent on the adaptability F_(i)(σ) of the node i, andthen executes type selection, i.e. updating of type selection inaccordance with the probability P_(i)(ρ) calculated.

The type selection stated above is repeated at a preselected period andis determined to have converged when, e.g. the adaptability F_(i)(σ) isgreater than c (c being a constant experimentally determined) inclusiveand when a particular type is continuously selected over a preselectedperiod of time, e.g. more than N consecutive periods, N being a naturalnumber. In the illustrative embodiment, the values of Ntyp,corresponding to the number of types, are assumed to be the same throughall the nodes and are determined by experiments beforehand.

Reference will be made to FIG. 6 for describing a specific procedure inwhich the node type selector 17 of the node i selects a type with theexpressions (1) through (4). As shown, the node type selector 17 setsthe initial value of the type of the own node i (step S1). The initialvalue of the type may be determined at random. Subsequently, when a nodetype signal from a neighboring node is received by the node type signalreceiver 18, type information contained in the node type signal andparticular to the neighboring node is stored in the node type signalreceiver 18.

The node type selector 17 reads out the stored type information of theneighboring node at a preselected repetition frequency while calculatingadaptabilities F_(i)(σ) with the expression (1) (step S2). In FIG. 6,F_(i)[t] denotes adaptability F_(i)(σ) at a time t in the node i; thetime t is representative of a discrete time (t=0, 1, 2, . . . ) whoseunit is a period.

The node type selector 17, when determined the adaptability F_(i)[t] atthe time t, compares the adaptability F_(i)[t] with adaptabilityF_(i)[t−1] determined at a time t−1 one period before the time t (stepS3). If the adaptability F_(i)[t] at the time t is greater than theadaptability F_(i)[t−1] at the time t−1, F_(i)[t]>F_(i)[t−1] (Yes, stepS3), then the node type selector 17 compares the adaptability F_(i)[t]with a random number δ lying in the range of 0<δ<1 (step S4).

If the adaptability F_(i)[t] is smaller than the random number δ,F_(i)[t]<δ (YES, step S4), then the procedure advances to a step S5.Otherwise (NO, step S4, F_(i)[t]≧δ, then the node type selector 17 dealswith adaptability F_(i)[t] at a time t+1 without updating the typeselection at the time t (step S2), as denoted with a connection 55.

Why a decision on the type selection is made on the basis of theadaptability F_(i)[t] is that, even when the adaptability F_(i)[t] hasincreased to a relatively great value in one period, the probabilitythat type selection will be updated is successfully increased. Again,this prevents type selection from failing to converge in some of thenodes.

On the other hand, if the adaptability F_(i)[t] at the time t is smallerthan the adaptability F_(i)[t−1] at the time t−1 or is not varied atall, F_(i)[t]<F_(i)[t−1], then the node type selector 17 calculatesprobability P_(i)(ρ) that a type ρ, where ρε{1, 2, . . . , Ntyp}, at thetime t will be selected. It is to be noted that P_(i)[t,ρ] denotes theprobability P_(i)(ρ) of selection of a type ρ at the time t.

The node type selector 17, having thus calculated the probabilities ofselection P_(i)[t,ρ] of the individual types at the time t, selects oneof the types, i.e. updates type selection in accordance with theprobabilities P_(i)[t,ρ] (step S5) and then repeats such type selectionat a preselected period. Subsequently, the node type selector 17determines whether or not the type has converged (step S6). When, e.g.the adaptability F_(i)(σ) is greater than or equal to c, which is aconstant determined by experiments, and when a particular type iscontinuously selected over, e.g. N periods, the node type selector 17determines that the type has converged (YES, step S6). This is the endof the procedure shown in FIG. 6. If the type has not converged (NO,step S6), then the procedure returns to the step S2 for dealing withtypes at the time t+1, as depicted with a connection 57.

The type of the own node i, selected by procedure of the node typeselector 17 described above, is fed to the node type signal transmitter19 and transmitted to neighboring nodes thereby.

The transmission timing calculator 12 shown in FIG. 2 will be describedin detail hereinafter. As briefly stated above, the transmission timingcalculator 12 is responsive to a received impulse signal or timingsignal Spr11 and type information 43 selected by the node type selector17 to perform an arithmetic operation for determining or defining atiming for transmitting an output impulse signal Sout11.

More specifically, as shown in FIG. 7 in a schematic block diagram, thetransmission timing calculator 12 includes an impulse signal demodulator21, a phase diffusion synchronization alliance circuit 22 and an impulsesignal modulator 23, which are interconnected as illustrated. Theimpulse signal demodulator 21 is adapted to demodulate the impulsesignal Spr11 received from another node in order to derive from itinformation representative of the spatial position of the other node anda timing signal 59 particular to the latter node.

The own node's type information 43 and the other node's timing signal 59output from the node type selector 17 and impulse signal demodulator 21,respectively, are input to the phase diffusion synchronization alliancecircuit 22, which includes a synchronization alliance circuit to bedescribed later. The phase diffusion synchronization alliance circuit 22is adapted to be responsive to the signals 43 and 59 to perform phasecalculation for determining or establishing the own node's transmissiontiming and then feed the resulting own node's phase signal Spr12 to theimpulse signal transmitter 13, synchronization decision circuit 14 anddata transmitter 15, FIG. 2, as well as to the impulse signal modulator23.

The impulse signal modulator 23 serves to generate the own node's timingsignal in response to the phase signal Spr12 output from the phasediffusion synchronization alliance circuit 22 and then modulate thetiming signal for thereby producing a modulated impulse signal 61. Themodulator 23 is, when generating the timing signal, operative inresponse to the impulse signal transmitter 13, FIG. 2. In theillustrative embodiment, the impulse signal transmitter 13 merelyfunctions as transmitting the modulated impulse signal 61 output fromthe transmission timing calculator 12 to other nodes.

FIG. 8 is a block diagram schematically showing a specific configurationof the phase diffusion synchronization alliance circuit 22. As shown,the phase diffusion synchronization alliance circuit 22 includes a phasecalculator 31, a collision ratio calculator 32, a stored stresscalculator 33, a stress response function calculator 34, a phaseresponse function characteristic determiner 35 and a synchronizationalliance circuit 36, which are interconnected as illustrated.

As briefly stated earlier, the transmission timing calculator 12performs an arithmetic operation for determining the transmission timingof the output impulse signal Sout11,. To determine the above timing, thetransmission timing calculator 12 uses, e.g. the following expressionmodeling nonlinear oscillation: $\begin{matrix}\begin{matrix}{\frac{\mathbb{d}{\theta_{i}(t)}}{\mathbb{d}t} = {\omega_{i} + {\sum\limits_{j \in {ei}}{{P_{j}(t)} \cdot {R\left( {{\Delta\theta}_{ij}(t)} \right)}}} +}} \\{{\sum\limits_{j \in {Yi}}{{P_{j}(t)} \cdot {H\left( {{\Delta\theta}_{ij}(t)} \right)}}} + {\xi\left( {S_{i}(t)} \right)}}\end{matrix} & (5) \\{{{\Delta\theta}_{ij}(t)} = {{{\theta_{j}(t)} - {\theta_{i}(t)}} = {- {\theta_{i}(t)}}}} & (6)\end{matrix}$

The above expression (5) is representative of a rule for varying, in thetime domain, the rhythm of nonlinear oscillation of the node i or ownnode in response to the input of the received impulse signal Spr11,which is derived from an output impulse signal Sout11 sent out fromanother node lying in the range of interaction.

Each node j may add the type information of the own node τ(j), or 43,resultantly output from the node type selector 17 to the impulse signalSout11 to transmit. In such a case, the expressions (5) and (6) define arule for varying, in the time domain, the phase state of the own node onthe basis of a timing signal representative of the phase information ofthe other node, and the type information of the other node and the ownnode. The own node transmits an impulse signal Sout11 via the impulsesignal transmitter 13, FIG. 2, in a particular phase or timing based ona phase state calculated by the expressions (5) and (6).

The meanings of symbols included in the expressions (5) and (6) and thedetails of the processing will be described hereinafter. In theexpression (5), the variable t is representative of a period of timecontinuous, but differs in meaning from the symbol t described as beingrepresentative of a discrete period of time or period in relation to thenode type selector 17 previously. The function θ_(i)(t) isrepresentative of a phase on the own node's nonlinear oscillation at thetime t. The function θ_(i)(t) is assumed to be constantly confined inthe range of 0≦θ_(i)(t)<2π by the operation of mod2π, i.e. a residualresulting from division by 2π.

Further, in the expression (5), Δθ_(ij)(t) is representative of a phasedifference produced by subtracting the phase θ_(i)(t) of the own node ifrom the phase θ_(j)(t) of the other node, as indicated by theexpression (6). Assuming that each node transmits an output impulsesignal Sout11 when the phase θ_(i)(t) is zero, then the own node i isallowed to monitor the phase difference Δθ_(ij)(t) only at the time whenthe output impulse signal Sout11 is received from the other node j, i.e.only one time for a single period. At this instant, while the phasedifference θ_(ij)(t) is equal to −θ_(i)(t), as also indicated by theexpression (6), it is assumed to be confined in the range of0≦Δθ_(ij)(t)<2π by executing mod2π after the addition of 2π forconvenience. The above assumption that each node transmits the outputimpulse signal Sout11 when the phase θ_(i)(t) is zero does not effectgenerality at all.

In the expression (5), ω_(i) denotes a specific angular frequencyparameter representative of the basic rhythm of each node and assumed tobe identical in the entire system by way of example. The functionP_(j)(t) is representative of a signal derived from the output impulsesignal Sout11 sent from the other node j, i.e. a received impulsesignal.

In each node i, the impulse signal transmitter 13 adds the own node'stype information τ(i) output from the node type selector 17 to animpulse signal Sout11 to be transmitted. The function P_(j)(t) isrepresentative of a timing signal left after the type information τ(j)has been separated from the received impulse signal 47. Morespecifically, the impulse signal receiver 11 separates the impulsesignal 47 received from another node j into the timing signal functionP_(j)(t) and type information τ(i).

Assume that the type information of neighboring nodes to be dealt withby the node type selector 17 of the own node i are τ(O1), τ(O2), . . . ,τ(On). Then, the impulse signal transmitter 13 transmits the impulsesignal Sout11 to a node range m hops (m being a natural number) apartfrom the own node i and broader than the node range n hops (n being anatural number smaller than m) apart from the own node i. For example,each node transmits an impulse signal Sout11 to a node range (n+1) hopsapart from the node. Although various methods are available for thetransmission of an impulse signal Sout11 to nodes m hops away from theown node, it is also possible to relay the impulse signal Sout11 byother nodes with a certain method. Alternatively, it is also possible totransmit the impulse signal on an electromagnetic wave having itsstrength great enough to directly reach the nodes m hops apart from theown node, in which case relaying is not necessary.

The function R(Δθ_(ij)(t)) is a phase response function representativeof a response characteristic that varies the basic rhythm of the ownnode in response to the input of the received impulse signal Spr11. Thefunction R(Δθ_(ij)(t)) has its characteristic nonlinearly varying theown node's phase θ_(i)(t) in a direction repulsing the other node'sphase. In the expression (5), X_(i) is representative of a node setlying in the interaction range of the own node other than elements thatbelong to a set Y_(i), which will be described later. Consequently, theterm including the function R(Δθ_(ij)(t)) has a dynamic characteristiccausing the own node's phase to repulse the other node's phase only ifthe received impulse signal Spr11 is sent out from another node lying inthe interaction range to be repulsed, i.e. a node lying in theinteraction range other than particular another other node to bedescribed later.

To determine whether or not the impulse signal is sent out from a nodeto be repulsed, the type information of the own node is compared withthat of the other node. If the other node's type is different from theown node's type, then it is determined that the impulse signal is sentout from a node to be repulsed, i.e. belonging to the node set X_(i).

The synchronization alliance function H(Δθ_(ij)(t)), like the phaseresponse function R(Δθ_(ij)(t)), is representative of a responsecharacteristic causing the basic rhythm of the own node to vary inresponse to the input of a received impulse signal, but differs from thefunction R(Δθ_(ij)(t)) in response characteristic. More specifically,the synchronization alliance function H(Δθ_(ij)(t)) has a nonlinearcharacteristic that synchronizes, i.e. causes particular another nodelying in a node range m hops apart from the own node and the own node tocoincide in phase. In the expression (5), Y_(i) is representative of anode set lying in the interaction range of the own node and expected tobe synchronized. Consequently, the term including the functionH(Δθ_(ij)(t)) has a dynamic characteristic that synchronizes the ownnode's phase only if the received impulse signal is sent out fromanother node lying in the interaction range and expected to besynchronized.

To determine whether or not the impulse signal is sent out from a nodeto be synchronized, the type information of the own node is comparedwith that of the other node. If the other node's type is identical withthe own node's type, it is then determined that the impulse signal issent out from a node to be synchronized, i.e. belonging to the node setY_(i).

The dynamic characteristic of the function H(Δθ_(ij)(t)) stated abovemay be implemented by, but not limited to, the following function form:$\begin{matrix}{{H\left( {{\Delta\theta}_{ij}(t)} \right)} = \left\{ \begin{matrix}{{\Delta\theta}_{ij}(t)} & {0 \leq {{\Delta\theta}_{ij}(t)} < \pi} \\{{{\Delta\theta}_{ij}(t)} - {2\pi}} & {\pi \leq {{\Delta\theta}_{ij}(t)} < {2\pi}}\end{matrix} \right.} & \begin{matrix}\left( {7\text{-}1} \right) \\\left( {7\text{-}2} \right)\end{matrix}\end{matrix}$

A stress response function ζ(S_(i)(t)) causes, when a relative phasedifference is small between the own node and the other node, stress tobe stored and causes a phase shift or phase state variation of randomsize to be executed in accordance with a stored stress value S_(i)(t).The relative phase difference mentioned above may be defined as:assuming a phase difference of Δθ_(ij) and a relative phase differenceof E, thenif Δθ_(ij) ≦π,E=Δθ _(ij)  (8)if Δθ_(ij) >π, E=2π−Δθ_(ij)  (9)

It will be seen from the above that the stress response functionζ(S_(i)(t)) is representative of a response characteristic to the storedstress value S_(i)(t).

Examples of the phase response function R(Δθ_(ij)(t)) and stressresponse function ζ(S_(i)(t)) will be described hereinafter. To beginwith, there will be described a collision between data transmissions, acollision ratio using the duration of a collision as a reference and acollision ratio using the number of times of collisions as a reference,which are terms relating to the above two functions R(Δθ_(ij)(t)) andζ(S_(i)(t)).

First, as for a collision between data transmissions, assume that theminimum time slot necessary for each node to transmit data is W_(min)and that a phase width corresponding to the time slot W_(min) is φc andcan be produced as a product of W_(min) and specific frequency parameterω_(i), i.e. φc=W_(min)·ω_(i). The size W_(min) of the time slot is aconstant parameter dependent on, e.g. the application of the system.

Further, assume that when a phase difference between a given node and aneighboring node lying in a spatial distance range capable of receivingan impulse signal is smaller than the phase width φc, it is determinedthat a collision has occurred between data transmissions. Morespecifically, when the phase difference of even one of a plurality ofreceived impulse signals Spr11 is smaller than the phase width φc, it isdetermined that a collision has occurred between data transmissions.

As for a collision ratio using the duration of a collision as areference, a function x_(i)(t) representative of whether or not acollision between data transmissions has occurred at a time t, asdetermined at each node, is produced by: $\begin{matrix}{{x_{i}(t)} = \left\{ \begin{matrix}1 & {collision} \\0 & {else}\end{matrix} \right.} & (10)\end{matrix}$

As shown, the function x_(i)(t) has a numerical value “1” if a collisionis happening at the time t, i.e. collision, expression (10)), orotherwise has a numerical value “0”, i.e. else, expression (10). Then, acumulative duration of collisions y_(i)(t) in n periods is produced byaccumulating, or time-integrating, the values x_(i)(t) over n periods:y _(i)(t)=∫_(−n·T) _(i) x _(i)(τ)dτ  (11)where T_(i) denotes the period of a node i. The cumulative duration ofcollisions y_(i)(t) is representative of the sum of periods of timeduring which the function x_(i)(t) takes a value of unity “1” in nperiods and can be produced by monitoring the value of the functionx_(i)(t).

A value c_(i)(t), produced by normalizing the cumulative collisionduration y_(i)(t) by the maximum cumulative collision duration, isrepresentative of the time ratio of collisions occurred in n periods andis referred to as a collision ratio in the illustrative embodiment. Themaximum cumulative collision duration is the maximum value of thecumulative collision duration y_(i)(T). Assuming that each node uses atime slot of a size W_(min) (=φc/ω_(i)) for transmission, then themaximum cumulative collision duration is n·W_(min) (=n·φc/ω_(i)).Therefore, the collision ratio c_(i)(t) is expressed as: $\begin{matrix}{{c_{i}(t)} = \frac{\omega_{i} \cdot {y_{i}(t)}}{n \cdot \phi_{c}}} & (12)\end{matrix}$

It should be noted that because the phase of each node varies inaccordance with the expression (5), the period T_(i) may take adifferent value period by period. Therefore, it is likely that thecumulative collision duration y_(i)(t) exceeds the maximum cumulativecollision duration n·W_(min), i.e, the collision ratio c_(i)(t) exceeds“1”. In the illustrative embodiment, collision ratios c_(i)(t) exceeding“1” are dealt with as “1”.

The definition of a collision ratio stated above does not giveconsideration to whether or not a plurality of collisions have occurredat the same time. The invention is not restricted thereto but a decisionmay, of course, be made on a plurality of simultaneous collisions.

For defining a collision ratio, use may also be made of, for example,the number of times of simultaneous collisions with the illustrativeembodiment, as will be described later. In addition, the collision ratiomay be defined with reference to collision time as described above, andalternatively to the number of collisions.

First, whether or not a collision has occurred is determined everyperiod. In this case, even when a collision has occurred a plurality oftimes during a single period, a count is “1”, i.e. only whether or not acollision has occurred is the matter to be considered.

Subsequently, the number of times of collisions occurred during nperiods, i.e. a cumulative number, or count, of collisions γ isdetermined. Thereafter, the cumulative number of collisions γ isnormalized by the maximum cumulative number of collisions, i.e. themaximum number of times of collisions that may occur during n periods,thereby producing a collision ratio:c _(i)(t)=γ/n  (13)

While the collision ratio produced by the expression (13) may exceed “1”as when the expression (12) is used, such a collision ratio is alsodealt with as “1”. While the above definition does not giveconsideration to whether or not a collision has occurred a plurality oftimes in a single period, a decision may, of course, be made on aplurality of collisions that may occur in a single period.

Let the duration of a collision and the number of times of collisionsincluded in the two different definitions stated above be collectivelyreferred to as a collision amount. Then, to determine a collisionamount, a cumulative collision amount during n periods is monitored andnormalized by the maximum cumulative collision amount to thereby producea collision ratio. The collision ratio calculator 32 calculates thecollision ratio c_(i)(t) expressed by the expression (12) or (13).

An example of the phase response function R(Δθ_(ij)(t)) which the phasecalculator 31 produces and the significance thereof will be describedhereinafter. The phase response function R(Δθ_(ij)(t)) may beimplemented by, but not limited to, the following function form:$\begin{matrix}{{R\left( {{\Delta\theta}_{ij}(t)} \right)} = \left\{ \begin{matrix}{\alpha \cdot \left( {{{\Delta\theta}_{ij}(t)} - \phi_{d}} \right)} & {{{\Delta\theta}_{ij}(t)} \leq \phi_{d}} \\0 & {\phi_{d} < {{\Delta\theta}_{ij}(t)} < {{2\pi} - \phi_{d}}} \\{\alpha \cdot \left( {{{\Delta\theta}_{ij}(t)} + \phi_{d} - {2\pi}} \right)} & {{{\Delta\theta}_{ij}(t)} \geq {{2\pi} - \phi_{d}}}\end{matrix} \right.} & \begin{matrix}\begin{matrix}\left( {14\text{-}1} \right) \\\left( {14\text{-}2} \right)\end{matrix} \\\left( {14\text{-}3} \right)\end{matrix}\end{matrix}$where φ_(d) and α denote constant parameters whose values are determinedby experiments. The constant parameter φ_(d) has its value greater thanthe minimum phase width φ_(c) inclusive necessary for data transmission,i.e. φ_(d)≧φ_(c).

The phase response function R(Δθ_(ij)(t)) has a nonlinear characteristiccausing the phase θ_(i)(t) of the own node i to vary in a direction inwhich a repulsive force acts on the phase of the neighboring node j.More specifically, the repulsive force acts when the relative phasedifference Δθ_(ij)(t) between the own node i and the neighboring node jis φ_(d). The phase response function R(Δθ_(ij)(t)) therefore obtains adynamic characteristic that makes the relative phase differenceΔθ_(ij)(t) mentioned above greater than the minimum phase width φ_(c)necessary for avoiding a collision.

The phase response function R(Δθ_(ij)(t)) may alternatively be producedby the following function form: $\begin{matrix}{{R\left( {{\Delta\theta}_{ij}(t)} \right)} = \left\{ {\begin{matrix}{\alpha \cdot \left( {{{\Delta\theta}_{ij}(t)} - \frac{2\pi}{p}} \right)} & {{{\Delta\theta}_{ij}(t)} \leq \frac{2\pi}{p}} \\{{{\beta\left( {c_{i}(t)} \right)} \cdot \Delta}{{\overset{\sim}{\theta}}_{ij}(t)}} & {\frac{2\pi}{p} < {{\Delta\theta}_{ij}(t)} < {{2\pi} - {p\quad{and}\quad\Delta{{\overset{\sim}{\theta}}_{ij}(t)}}} < \frac{\pi}{p}} \\{{\beta\left( {c_{i}(t)} \right)} \cdot \left( {{\Delta{{\overset{\sim}{\theta}}_{ij}(t)}} - \frac{2\pi}{p}} \right)} & {\frac{2\pi}{p} < {{\Delta\theta}_{ij}(t)} < {{2\pi} - {p\quad{and}\quad\Delta{{\overset{\sim}{\theta}}_{ij}(t)}}} > \frac{\pi}{p}} \\{\alpha \cdot \left( {{{\Delta\theta}_{ij}(t)} - \frac{\left( {p - 1} \right)\pi}{p}} \right)} & {{{2\pi} - \frac{2\pi}{p}} \leq {{\Delta\theta}_{ij}(t)}}\end{matrix}{where}} \right.} & \begin{matrix}\begin{matrix}\begin{matrix}\quad \\\quad\end{matrix} \\\left( {15\text{-}1} \right)\end{matrix} \\\begin{matrix}\begin{matrix}\begin{matrix}\begin{matrix}\begin{matrix}\begin{matrix}\quad \\\left( {15\text{-}2} \right)\end{matrix} \\\quad\end{matrix} \\\left( {15\text{-}3} \right)\end{matrix} \\\quad\end{matrix} \\\left( {15\text{-}4} \right)\end{matrix} \\\quad\end{matrix}\end{matrix} \\{{\beta\left( {c_{i}(t)} \right)} = {b \cdot \left( {1 - {c_{i}(t)}} \right)^{2}}} & {\quad(16)}\end{matrix}$where Δ{tilde over (θ)}_(ij)(t) denotes${{{\Delta\theta}_{ij}(t)}\left( {{mod}\frac{2\pi}{p}} \right)},$i.e. a residue resultant from dividing Δθ_(ij)(t) by $\frac{2\pi}{p}.$

The phase response function R(Δθ_(ij)(t)) represented by the expressions(15-1) through (15-4) and (16) allows a uniform phase difference to beset up between neighboring nodes. In the above expressions, p denotes aconstant parameter for determining the uniform phase difference. As forthe phase response function with such a form, by equalizing the constantparameter p and the number of types Ntyp, it is possible for each nodeto form substantially the same phase difference pattern between it andNtyp different kinds of neighboring nodes; the phase difference patterndivides a single period into substantially Ntyp.

Hereinafter will be described a specific example of the stress responsefunction ζ(S_(i)(t)) produced by the sequential operations of the storedstress calculator 33 and stress response function calculator 34 and thesignificance of the stress response function. The stress responsefunction ζ(S_(i)(t)) may be expressed as:${q\left( {S_{i}(t)} \right)} = \left\{ {{\begin{matrix}{\mu} & {{with}\quad{prob}\quad{S_{i}(t)}} & {\quad\left( {18\text{-}1} \right)} \\0 & {{{with}\quad{prob}\quad 1} - {S_{\quad i}(t)}} & {\quad\left( {18\text{-}2} \right)}\end{matrix}{S_{i}(t)}} = {\int_{ts}^{t}{{s\left( {c_{i}(\tau)} \right)}{\mathbb{d}\tau}\quad(19)}}} \right.$

In the above expression (19), the function s(c_(i)(t)) is representativeof a stress value relating to the collision ratio c_(i)(t) at the time tand may be configured such that the higher the collision ratio c_(i)(t),the greater the stress value. For example, use may be made of asigmoidal function or similar nonlinear function for causing the stressvalue to sharply increase with an increase in collision ratio c_(i)(t).

The function S_(i)(t) defined by the expression (19) is representativeof a value produced by storing or time-integrating stress valuess(c_(i)(t)) at times t. A time interval for storage is between a time tsat which a random phase shift is executed in accordance with a stressvalue S_(i)(t) stored previously and the current time t. Morespecifically, the function S_(i)(t) is reset when a random phase shiftis executed, and again starts storing stress values s (c_(i)(t)). Whenthe time t is provided in a discrete form, the integration of thefunction S_(i)(t) may be implemented as a sum of stress values S_(i)(t)at each time. The stored stress S_(i) (t) is calculated by the storedstress calculator 33.

The function q (S_(i)(t)) defined by the expression (18-1) or (18-2)produces a random number with a probability corresponding to the storedstress value S_(i)(t). The function produces a value p at theprobability of S_(i)(t) and produces zero at the probability of1−S_(i)(t). The value μ is a random number lying in the range of ε≦μ<δwhere ε and δ are constant parameters determined by experiments.

The stress response function ζ(S_(i)(t)) evaluates the stored stressvalue S_(i)(t) every n-th period and produces a random value μ or zerowith the probability according thereto. The stress response functionζ(S_(i)(t)) is calculated by the stress response function calculator 34.

It follows from the above that, as the expression (5) indicates, byintroducing the stress response function ζ(S_(i)(t)) in the model ofnonlinear oscillation, it is possible to evaluate the stored stressvalue. S_(i)(t) every n-th period and execute the random phase shiftwith probability based on the evaluated stress value S_(i)(t). Morespecifically, the more the stress values caused by collision, the higherthe probability with which the random phase shift is executed. At timesother than those corresponding to the integral multiples of the nperiods, the stress response function value ζ(S_(i)(t)) is zero, so thatthe random phase shift is not executed. However, it should be noted thatthe period of time during which the stress is stored is not limited tothe n periods stated above, but may be the time interval between thetime ts at which a random phase shift has been executed previously andthe current time t. This means that, e.g. when the stress value s(c_(i)(t)), even if small, is continuously accumulated over a period oftime longer than the n periods, the cumulative stress value S_(i)(t)ultimately becomes extensive and may cause the random phase shift to beexecuted.

The phase calculator 31 uses the stress response function valueζ(S_(i)(t)) to calculate the phase θ_(i)(t) determined by the expression(5).

The transmission timing calculator 12, suitably executing the sequencedescribed above, may be implemented by software or hardware executingthe operations with electronic circuits, or even by the combination ofsoftware and hardware.

The operation defined by the expression (5) may be implemented on acommunication node by general-purpose software, e.g. a Runge-Kuttamethod, which is one of methods using a difference expression, orrecurrence expression, resulting from the differentiation of adifferential expression, or making the continuous time variable tdiscrete, i.e. quantization, to calculate a change, or temporaldevelopment, of a state variable. Runge-Kutta method is taught as ageneral background knowledge in H. Togawa, “Scientific EngineeringCalculation Handbook by UNIX Workstation—Volume Fundamental, C-LanguageVersion” published by Saiensu-sha Co., Ltd., Tokyo, for example.

Each node performs the operations represented by the expressions (5) and(6), so that an adequate phase relation is established between nodeslying in the interaction range. For example, assuming a condition ofm=n+1, then a given node i selects a type different from the type ofnodes lying in the n-th neighboring range, establishing a significantphase difference. Also, the node i is synchronous or coincident in phaseto or with, among a set of nodes lying in the (n+1)-th neighboring rangeexcept for nodes lying in the n-th neighboring range, a node selectingthe same type as the own node i. If such a condition is establishedthroughout the entire nodes, then the nodes of a node set lying in then-th neighboring range other than the node i and held in a positionalrelation free from a collision between their transmissions issynchronized to each other. It follows that the phase difference whichthe node i forms between it and the other nodes lying in the n-thneighboring range can be increased by an amount corresponding to thenumber of such nodes synchronized in phase to each other, allowing thenode i to obtain a greater time slot than conventional.

As stated above, in the illustrative embodiment, the node type selector17 selects the type information of the own node on the basis of the typeinformation of neighboring nodes while the transmission timingcalculator 12 implements, based on the output of the node type selector17 and the timing signals of neighboring nodes, the transmission timingsof a plurality of nodes, i.e. effects phase diffusion synchronizationalliance. The illustrative embodiment therefore successfully realizesoptimum time-division telecommunication even when nodes are not locatedin a lattice pattern.

Consequently, the nodes of a node set lying in the n-th neighboringrange other than the node i and held in a positional relation free froma collision between their transmissions are synchronized in phase toeach other. It follows that the phase difference which the node iestablishes between it and the other nodes lying in the n-th neighboringrange can be increased by an amount corresponding to the number of suchnodes synchronized in phase to each other, allowing the node i to obtaina broader time slot than those obtainable with the conventional methods.

A second or alternative embodiment of the present invention will bedescribed hereinafter. The first embodiment described above isconfigured such that, after type selection by the node type selector 17has converged, the transmission timing calculator 12 calculates atransmission timing on the basis of the output of the node type selector17. Stated another way, in the first embodiment, node type selection isonce separated from transmission timing calculation and repeatedlyexecuted as preprocessing. By contrast, the second embodiment executesnode type selection and transmission timing calculation in parallel.

FIG. 9 shows a specific configuration of a transmission timingcalculator 212 unique to the alternative embodiment. The alternativeembodiment may be the same as the previous embodiment except for the twomajor points. First, the alternative embodiment does not include thenode type signal receiver 18 nor the node type signal transmitter 19,but uses, from the beginning of the execution, the impulse signalreceiver 11 and impulse signal transmitter 13 for transmitting andreceiving an impulse signal with node type information, such as nodetype information of another node j and nodes neighboring it, added tothe impulse signal. Second, the alternative embodiment inputs, everytime a node type selector 217 updates type selection, the result of theupdated type selection to the transmission timing calculator 212 so asto cause the latter to reflect the result on the calculation of thetransmission timing of an impulse signal.

The following description will concentrate mainly on the operations ofthe node type selector 217 and transmission timing calculator 212 uniqueto the alternative embodiment. Structural elements like those of thefirst embodiment are not shown, and detailed description thereon willnot be made in order to avoid redundancy.

The transmission timing calculator 217 includes an impulse signalreceiver 211, which is adapted to receive an impulse signal 63 emittedfrom a neighboring node. In the alternative embodiment, the impulsesignal 63 conveys the type information of a neighboring node addedthereto, as stated above. Therefore, the impulse signal receiver 211separates type information contained in the received impulse signal 63and then delivers a signal 65 representing the type information andimpulse signal to the node type selector 217. The node type selector 217is adapted to be responsive to the signal 65 to select the typeinformation of the own node and feeds node type information 67 to thetransmission timing calculator 212 every time it selects or updates thenode type information.

It is to be noted that the type information added to the signal 65including the impulse signal 63 and output from the impulse signalreceiver 211 contains not only the own node type information τ(i) butalso the type information received from the neighboring node. To selecttype information, the node type selector 217 also uses the expressions(1) through (4) described in relation to the previous embodiment.

The transmission timing calculator 212 is adapted for receiving thesignal 67 including the type information and another node's impulsesignal from the node type selector 217 to determine a timing fortransmitting an output impulse signal Sout11. The method of calculatinga transmission timing may be the same as the method described inconnection with the previous embodiment and will not be describedspecifically in order to avoid redundancy.

Assume that the type information of neighboring nodes to be dealt withby the node type selector 17 of the own node are τ(O1), τ(O2), . . . ,τ(On). Then, an impulse signal transmitter 213, having its input port 69interconnected to the node type selector 217, is adapted fortransmitting the impulse signal 71 to a node range which is m hops apartfrom the own node and broader than the node range which is n hops apartfrom the own node, as stated earlier in connection with the previousembodiment. For example, each node transmits an impulse signal to a noderange (n+1) hops apart from the node. Various methods are available forthe transmission of an impulse signal to nodes m hops away from the ownnode. The transmission may be implemented by relaying the impulse signalby other nodes by a certain method. Alternatively, the impulse signalmay be transmitted on an electromagnetic having its strength greatenough to directly reach the nodes m hops apart from the own node, inwhich case relaying is not necessary, of course.

A specific operation of the alternative embodiment will be describedwith reference to FIG. 10, which demonstrates the type selectionprocedure executed by the node type selector 217 by using theexpressions (1) through (4) in connection with the selection processingand transmission timing calculation. FIG. 10 partially includes some ofthe steps shown in FIG. 6 and designated with the same step numbers, anddetailed description thereof will not be made in order to avoidredundancy.

As shown in FIG. 10, the node type selector 217 determines adaptabilityF_(i)[t] at a time t and then determines whether or not the adaptabilityF_(i)[t] is greater than adaptability F_(i)[t−1] determined at a timet−1 (step S3), as in the previous embodiment. If the adaptabilityF_(i)[t] is greater than the adaptability F_(i)[t−1] (YES, step S3),then the node type selector 217 determines whether or not theadaptability F_(i)[t] is smaller than a random number δ (step S1). Ifthe adaptability F_(i)[t] is equal to or greater than the random numberδ (NO, step S11), then, as depicted with a connection 73, the node typeselector 217 does not update the type selection at the time t, butcalculates adaptability at the next time t+1 and reports such processingto the transmission timing calculator 212 for thereby causing it tocalculate a transmission timing in accordance with the non-updated typeinformation (step S13).

On the other hand, if the adaptability F_(i)[t] is equal to or smallerthan the adaptability F_(i)[t−1] (NO, step S3) or F_(i)[t] is smallerthan the random number δ (YES, step S11), then the node type selector217 calculates the probability of selection P_(i)[t,ρ] of each type ρand then selects one of the types, i.e. updates data selection on thebasis of the selection probabilities of the individual types ρ thuscalculated (step S12). Subsequently as depicted with a connection 79,the node type selector 217 reports the updating of the type selection tothe transmission timing calculator 212 for thereby causing it tocalculate a transmission timing based on the updated type selection(step S13).

In the step S6 following the step S12, whether or not the type selectionprocessing by the node type selector 217 has converged is determined inthe same manner as in the previous embodiment. When such processingconverges, a type to be selected by the own node is fixed. This is theend of the type selection procedure. At this instant, in FIG. 10, onlythe operation of the transmission timing calculator 212 is executed. Ifdesired, when a preselected period of time elapses since the conversionof the node type selection processing, i.e. when neighboring nodes arealso expected to be in a converged state, only the type information τ(i) of the own node i may be added to an impulse signal to betransmitted.

The alternative embodiment achieves the same advantages as the previousembodiment. In addition, the alternative embodiment allows a nodeconfiguration to be scaled down because it does not include a node typetransmitter/receiver.

A third, or further alternative embodiment of the present invention willbe described hereinafter. The third embodiment is identical with thefirst and second embodiments except for the phase calculating method ofthe transmission timing calculator. More specifically, the thirdembodiment differs from the second and third embodiments as to theexpressions used by the transmission timing calculators 12 and 212 forthe calculation of a phase.

In the third embodiment, the transmission timing calculator 12 or 212generates a pseudo-phase signal by use of a virtual phase model inaccordance with, e.g. the following expressions: $\begin{matrix}{\frac{\mathbb{d}{\theta_{i}(t)}}{\mathbb{d}_{t}} = {\omega_{i} + {\frac{K_{x}}{N_{x}}{\sum\limits_{j \in {Xi}}{R\left( {{\Delta\theta}_{ij}(t)} \right)}}} + {\frac{K_{y}}{N_{y}}{\sum\limits_{j\overset{.}{\in}{Yi}}{H\left( {{\Delta\theta}_{ij}(t)} \right)}}} + {\xi\left( {S_{i}(t)} \right)}}} & \left( {20\text{-}1} \right) \\{{{\Delta\theta}_{ij}(t)} = {{\theta_{j}(t)} - {\theta_{i}(t)}}} & \left( {20\text{-}2} \right)\end{matrix}$where N_(x) and K_(x), included in the member including the phaseresponse function R(Δθ_(ij)(t)), respectively denote the number ofelements constituting a node set X_(i) and an association constantparameter, and N_(y) and K_(y), included in the member including thesynchronization alliance function H(Δθ_(ij)(t)), respectively denote thenumber of elements constituting a node set Y_(i) and an associationconstant parameter.

Thus, in the third embodiment, an impulse signal is used as aninteraction signal while a pseudo-phase signal is used for thecalculation of a transmission timing. The association constantparameters K_(x) and K_(y) are parameters respectively determining thedegree of contribution of the member including the functionR(Δθ_(ij)(t)) and that of the member including the functionH(Δθ_(ij)(t)) to the variation of the phase in the time domain. Theassociation constants K_(x) and K_(y) may be determined by experiments.

As stated above, the third embodiment achieves the same advantages asthe first and second embodiments. In addition, by generating apseudo-phase signal by using a virtual phase model, the third embodimentenhances the accuracy of phase calculation assigned to the transmissiontiming calculator 12 or 212 for thereby further stabilizing theestablishment of a phase relation between nearby nodes.

A still further alternative, fourth embodiment of the present inventionwill be described hereinafter. In the first, second and thirdembodiments, it is assumed that the number of types Ntyp stored in thenode type selectors 17 or 217 is the same throughout the nodes of thetelecommunications system and is determined by experiments beforehand.By contrast, in the fourth embodiment to be described, each nodeadditionally includes a number-of-types determining circuit forautonomously determining the number of types at the time of typeselection and can therefore store a particular number of types Ntyp.Further, the number of types Ntyp is determined during the processing ofthe node type selector. Consequently, even when the disposition densityof nodes, for example, is locally different in a telecommunicationsnetwork, the number of types of nodes Ntyp autonomously adapts to thedensity node by node, allowing each node to obtain a particular timeslot divided by a number adequate for each area.

FIG. 11 is a schematic block diagram showing the major part of a node 10a unique to the fourth illustrative embodiment. As shown, the node 10 aincludes a number-of-types determiner 301 connected to a node typeselector 317. It is to be noted that the circuitry shown in FIG. 11corresponds to the circuitry shown in FIG. 2 except that thenumber-of-types determiner 301 is added. In addition, FIG. 11 does notspecifically show the transmission timing calculator 12 and othercircuits shown in FIG. 2 merely in order to clearly indicate therelation between the number-of-types determiner 301 and node typeselector 317. The structural features of the fourth embodiment may, ofcourse, be applied to the second or the third embodiment, if desired.

The node type selector 317 is adapted to select the type of the own nodeon the basis of the type information of neighboring nodes stored in thesame manner as in the first embodiment, while feeding adaptabilityF_(i)[t], 75, determined at each time t to the number-of-typesdeterminer 301. The number-of-types Ntyp determined by thenumber-of-types determiner 301 is input to the node type selector 317 asdepicted with a connection 77. If the number of types Ntyp has not beenupdated over a predetermined period of time, then the node type selector317 determines that the number of types Ntyp has been converged andfixed, and selects the own node's type by use of the fixed number oftypes as in the first embodiment.

More specifically, upon receiving the adaptability F_(i)[t] input fromthe node type selector 317 at each time t and if the maximumadaptability maxFi is not updated over preselected part of apredetermined period, the number-of-types determiner 301 determines astress value zi by means of the expression: $\begin{matrix}{z_{i} = {1 - \frac{\sum\limits_{\lambda = 0}^{M}{F_{i}\left\lbrack {t - \lambda} \right\rbrack}}{M + 1}}} & (21)\end{matrix}$where the second member of the right side denotes the mean value of theadaptabilities F_(i)[t] to occur when the maximum value maxFi is notupdated over the predetermined period of time. The adaptability F_(i)[t]is a variable lying in the range of 0<F_(i)(σ)≦1. Therefore, the stressvalue zi is representative of the mean value of non-adaptability tooccur when the maximum value maxFi is not updated over the predeterminedperiod of time.

When a cumulative stress value Zi exceeds a threshold value ε, thenumber-of-types determiner 301 updates the number of types Ntyp andreports the resulting new number 77 of types to the node type selector317.

Reference will be made to FIG. 12 for describing a specific procedure inwhich the fourth embodiment causes each node i to autonomously determinethe number of types Ntyp. As shown, assume that the number of types Ntypinitially stored in anode i is Nst (step S21). The initial value Nst isa constant parameter determined by experiments beforehand and may be “5”at all nodes by way of example.

After the step S21, the node type selector 317 starts calculatingadaptability F_(i)[t] as in the first embodiment (step S22). At the sametime, the node type selector 317 delivers adaptability F_(i)[t]determined at each time t to the number-of-types determiner 301. Everytime the number-of-types determiner 301 receives the adaptabilityF_(i)[t] of each period calculated by the node type selector 317, thedeterminer 301 stores the adaptability F_(i)[t] and sequentially storesconsecutive adaptabilities up to M periods before the current time t{F_(i)[t], F_(i)[t−1], F_(i)[t−2], . . . , F_(i)[t−M]} (step S23).

Subsequently, the number-of-types determiner 301 determines the maximumvalue maxFi of a set of adaptabilities {F_(i)[t], F_(i)[t−1],F_(i)[t−2], . . . , F_(i)[t−M]} stored therein and holds the maximumvalue maxFi (step S24). At this instant, the number-of-types determiner301 compares the maximum adaptability maxFi with the adaptabilityF_(i)[t] at the current time t on a period basis, and updates themaximum adaptability maxFi if it is smaller than the currentadaptability F_(i)[t]. It should be noted that if the currentadaptability at the time t is “1” when the maximum adaptability maxFi is“1”, then the subsequent steps are executed on the assumption that themaximum adaptability has been updated.

When the maximum adaptability maxFi is not updated over thepredetermined period of time, e.g. a plurality (L) of consecutiveperiods, L being a natural number, a stress value represented by theexpression (21) indicated above is produced (steps S25 and S26). Itshould be noted that the expression (21) is only illustrative and may bereplaced with any other suitable expression.

The stress value zi is calculated every time the maximum value maxFi isnot updated over the predetermined period of time, and is added to thevariable Zi representative of a cumulative stress value which isinitially zero (step S27). When the cumulative stress value Zi becomesgreater than the threshold value ε (YES, step S28), the number of typesNtyp is updated with probability δ (step S29). It is to be noted that εand δ are constant parameters determined by experiments. At the sametime, the cumulative stress value Zi is reset to zero.

The number of types Ntyp is updated in accordance withNtyp[t+1]=Ntyp[t]+1, where Ntyp[t] denotes the number of types at a timet.

If the number of types is not updated over a predetermined period oftime, as determined by the procedure stated above, it is determined thatthe number of types has converged. After such a procedure, thetransmission timing calculator 12, FIG. 2, operates in the same manneras in the first embodiment when the processing of the node type selector317 converges.

The procedure of the fourth embodiment shown in FIG. 12 has beendescribed as applied to the first embodiment. It may alternatively beapplied to the second or the third embodiment, if desired.

As stated above, in accordance with the fourth embodiment, each node 10a includes the number-of-types determiner 301 for autonomouslydetermining the number of types of nodes Ntyp. Therefore, even when thedisposition density of nodes, for example, is locally different in atelecommunications network, the number of types of nodes Ntypautonomously adapts to the density node by node, allowing each node toobtain a particular time slot divided by a number adequate for each areaand therefore enhancing efficient communication. Of course, the fourthembodiment achieves the same advantages as the first, second and thirdembodiments as well.

A fifth, still further embodiment of the present invention will bedescribed hereinafter with reference also made to FIG. 11. The fifthembodiment is similar to the fourth embodiment described above exceptfor the following. The fourth embodiment determines the number of typesNtyp by sequentially increasing it from the initial value Nst in theevent of type selection, so that the number of types Ntyp increased isnot decreased afterward. This, however, gives rise to a problem that,because each node 10 a increases the number of types Ntyp independentlyof the other nodes, it is likely that the number of types Ntyp becomesgreater than the optimum value and converges. To solve this problem, inthe fifth embodiment to be described, the number-of-types determiner 301is designed for not only increasing the number of types Ntyp but alsodecreasing it, as the case may be.

More specifically, in the fifth embodiment, the number-of-typesdeterminer 301 is adapted to selectively increase or decrease the numberof types of nodes in accordance with the time-serial adaptabilityinformation 75 fed from the node type selector 317. The method ofincreasing the number of node types executed by the determiner 301differs from the method of the fourth embodiment, and will also bedescribed specifically. While the sequence of steps shown in FIG. 11 isapplied to the node configuration of the first embodiment shown in FIG.1, it is similarly applicable to the node configuration of the second orthe third embodiment.

In the fifth embodiment, the number-of-types determiner 301 isstructured to execute the processing, which will be described later, inaccordance with adaptability F_(i)[t] fed from the node type selector317 at each time t, thereby increasing or decreasing the number of typesNtype. The number-of-types determiner 301 then reports the resulting newnumber 77 of types Ntyp to the node type selector 317.

How the number-of-types determiner 301 of the fifth embodiment allowsthe own node i to autonomously determine the number of types Ntyp willbe described with reference to FIGS. 13 and 14. FIGS. 13 and 14demonstrate procedures for decreasing and increasing the number of typesNtyp, respectively.

As shown in FIG. 13, the number of types Ntyp initially stored in thenode i is set to Nst (step S31). Again, the initial value Nst is aconstant parameter determined by experiments beforehand and may be “5”at all nodes by way of example. After the step S31, the node typeselector 317 starts calculating adaptability F_(i)[t] as in the firstembodiment (step S32) while feeding the adaptability F_(i)[t] thuscalculated to the number-of-types determiner 301.

Every time the number-of-types determiner 301 receives the adaptabilityF_(i)[t] calculated by the node type selector 317 every period, thedeterminer 301 stores the adaptability F_(i)[t] and sequentially storesconsecutive adaptabilities up to M periods before the current time t{F_(i)[t], F_(i)[t−1], F_(i)[t−2], . . . , F_(i)[t−M]} (step S33).Subsequently, the number-of-types determiner 301 determines the maximumvalue maxFi of the set of adaptabilities thus stored, or an adaptabilityset as referred to hereinafter, (step S34).

Generally, two or more of the elements (F_(i)[t], F_(i)[t−1],F_(i)[t−2], . . . , F_(i)[t−M]), constituting the adaptability set, maygive the maximum value maxFi. Stated another way, the adaptability mayhave the maximum value maxFi at a plurality of times. In light of this,the illustrative embodiment determines a reference time tp for givingthe maximum value maxFi, as will be described hereinafter.

If the maximum value maxFi is equal to “1” (YES, step S36), the latestone of the times included in the adaptability set and giving the maximumvalue maxFi is selected as a reference time tp (step S36). On the otherhand, if the maximum value maxFi is smaller than “1” (NO, step S35),then the oldest time farthest from the current time t is selected as areference time tp (step S37).

After the step S36 or S37, there is calculated a stress value zi by thefollowing expression (step S38): $\begin{matrix}{z_{i} = {1 - \left( \frac{\sum\limits_{\lambda = 0}^{M}{{\exp\left( {{- c} \cdot \lambda} \right)} \cdot {F_{i}\left\lbrack {t - \lambda} \right\rbrack}}}{\sum\limits_{\lambda = 0}^{M}{\exp\left( {{- c} \cdot \lambda} \right)}} \right)^{2}}} & (22)\end{matrix}$where exp(*) denotes an exponential function, c denotes a constantparameter determined by experiments, and the parenthesized member of thesecond term on the right side denotes a weighted mean of adaptabilitiesF_(i)[t].

Assuming that c is greater than zero, then a weighting factor assignedsequentially increases in order of F_(i)[t], F_(i)[t−1], . . . ,F_(i)[t−M]. Stated in another way, the closer the adaptability to thecurrent time t, the higher the degree of contribution to the stressvalue is. Further, because the adaptability F_(i)[t] is a variable lyingin the range of 0<F_(i)(σ)≦1, the stress value Zi is representative ofnon-adaptability calculated on the basis of the weighted mean ofadaptabilities F_(i)[t].

If a difference between the current time t and the reference time tpgiving the maximum value maxFi is equal to or greater than a preselectedperiod of time (YES, step S39), then the stress value zi is added to thevariable Zi representative of a cumulative stress value (step S40). Thepreselected period of time mentioned above is assumed to be a plurality(L) consecutive periods, L being a natural number. The initial value ofthe stress value Zi is zero, i.e.if t−tp≧L, Zi[t+1]=Zi[t]+zi[t],  (23)where Zi[t] and zi[t] respectively denote a cumulative stress value anda stress value at the time t.

The difference t−tp is evaluated every period. Every time the relationof t−tp≧L is satisfied, the stress value zi is added to the cumulativestress value Zi. Assume that the cumulative stress value Zi increasesabove the threshold value ε (YES, step S41). Then, it is determined(step S42) whether or not the number of types Ntype is smaller than Ni(max), which is a constant parameter giving the maximum value of thenumber of types and determined by experiments. If the answer of the stepS42 is YES, then the number of types Ntyp is updated, or increased, withprobability δ (step S43). At the same time, the cumulative stress valueZi is rest to zero. In the step S43, the number of types is updated bythe following expression:Ntyp[t+1]=Ntyp[t]+1,  (24)where Ntyp[t] denotes the number of types at the time t.

By the above procedure, the number of types increases with respect toprobability every time the cumulative stress value Zi exceeds thethreshold value ε. The processing represented by the expressions (23)and (24) has the following significance.

When the maximum value maxFi is equal to “1”, the difference t−tp isrelatively small and, in many cases, smaller than the preselected periodL, maintaining the cumulative stress value Zi the same. Conversely, whenthe maximum value maxFi is smaller than “1”, the difference t−tp isrelatively great and, in many cases, greater than the period of time Linclusive, causing a stress value zi to be added to the cumulativestress value Zi. Therefore, so long as maxFi is smaller than “1”, stressvalues are frequently added to the cumulative stress value Zi. However,when maxFi becomes “1”, the cumulative stress value Zi stops increasingbecause hardly any stress value zi is added thereto. This is successfulto implement a condition wherein when maxFi becomes “1”, the number oftypes stops increasing.

Next, the procedure for decreasing the number of types executed by thenumber-of-types determiner 301 will be described with reference to FIG.14. As shown, after the initial value Nst of the number of types of thenode i has been stored (step S51), the node type selector 317 calculatesadaptability F_(i)[t] (step S52) while the number-of-types determiner301 stores adaptabilities F_(i)[t] up to M periods before the currenttime t {F_(i)[t], F_(i)[t−1], F_(i)[t−2], . . . , F_(i)[t−M]} (stepS53). Such consecutive adaptabilities will be referred to as anadaptability set hereinafter.

Subsequently, the number-of-types determiner 301 determines whether ornot the elements of the above adaptability set satisfy a certaincondition each (step S54) and, if the answer of the step S54 is YES,reduces the number of types (step S55), as represented by:$\begin{matrix}{{{{{if}\quad\frac{\sum\limits_{\lambda = 0}^{M}{F_{i}\left\lbrack {t - \lambda} \right\rbrack}}{M + 1}} = {{1\quad{and}\quad{Nst}} < {{Ntyp}\lbrack t\rbrack}}},{then}}{{{Ntyp}\left\lbrack {t + 1} \right\rbrack} = {{{Ntyp}\lbrack t\rbrack} - 1}}} & (25)\end{matrix}$

The above condition means that the elements of the adaptability set,i.e. the adaptabilities over the past plural (M) periods as counted fromthe current time t all be “1” and that the current number of typesNtyp[t] be greater than the initial value Nst. If adaptability is “1”,which is the maximum value, over (M+1) consecutive periods, i.e. aninterval between a time M periods before the current time and thecurrent time, then it is likely that the number of types is greater thanand settled at the optimum value. In this case, the number-of-typesdeterminer 301 reduces the number of types in accordance with theexpression (25) for thereby allowing the number of types to converge tothe optimum value more frequency than in the fourth embodiment andtherefore implementing more stable operations.

The condition that adaptability be continuously “1” over the (M+1)periods, as defined in the expression (25), is only illustrative and maybe replaced with a condition that adaptability be continuously greaterthan a preselected threshold value over a preselected period of time, ifdesired.

With the above procedure, the fifth embodiment determines that when thenumber of types is not updated for more than a predetermined period oftime, the number of types has converged or is fixed. Subsequently, thefifth embodiment causes the transmission timing calculator to operateafter the operation of the node type selector.

As stated above, the fifth embodiment additionally includes thenumber-of-types determiner 301 for allowing the own node to autonomouslydetermine the number of types N-typ, i.e. selectively increase ordecrease the number of types N-typ. Therefore, in a telecommunicationsnetwork including a plurality of nodes, even when the distributiondensity of nodes, for example, is different from area to area, thenumber of types of nodes Ntyp autonomously adapts to the density node bynode more stably than the fourth embodiment, allowing each node toobtain a particular time slot divided by a number adequate for each areaand hence further enhancing efficient communication. The fifthembodiment, of course, achieves the same advantages as the first tofourth embodiments as well.

The first to fifth embodiments shown and described may be changed ormodified, as will be described hereinafter. While in the firstembodiment, the specific angular frequency parameter ω_(i) is assumed tobe uniform in the entire system, it may, of course, differ from one nodeto another node. For example, the specific angular frequency parameterω_(i) may be slightly distributed around a reference value in accordancewith the Gaussian distribution or similar probability distribution.

Although the first to fifth embodiment all assume a system in which anumber of spatially distributed nodes transmit and receive data witheach other by radio, the present invention is similarly applicable to asystem in which spatially distributed nodes transmit and receive datawith each other by wire, e.g. Ethernet (trade name) or similar wired LANsystem. Further, the present invention is applicable even to a networkin which different kinds of nodes, e.g. wire-connected sensors andactuators or servers exist together or a network in which wire-connectednodes and radio or wireless nodes exist together.

The present invention may be used as a communication protocol thatallows routers arranged on the Internet to transmit and receive data ofa routing table at different timings from each other. Here, a routerrefers to a relaying apparatus configured to route each informationflowing on a network to a particular destination, i.e. having acommunication path selecting function. Also, a routing table refers to acommunication path selection rule to be referenced at the time ofrouting of the above information. To implement efficient communication,it is necessary to update the routing table in succession in accordancewith, e.g. modifications on a network or local traffic changes. For thispurpose, a number of routers present on a network transmit and receive arouting table with each other at predetermined intervals.

However, it is known that despite that each router transmits a routingtable independently of the other routers, transmissions from differentrouters are gradually brought into synchronization or collision, astaught in Floyd, S. and Jacobson V. “The Synchronization of PeriodicRouting Messages”, IEEE/ACM Transactions on Networking, Vol. 2, No. 2,pp. 122-136, April 1994, as a general background knowledge. Thisdocument proposes to cope with the above synchronization by randomlyvarying the processing period of each node as to a communicationprotocol for the transmission and reception of a routing table anddescribes advantages achievable with such a method. However, the methodproposed in the above document basically relies on randomness and istherefore not sufficiently effective.

By contrast, the present invention successfully solves the problemstated above by allowing nearby routers to autonomously adjust a timeslot for the transmission of a routing table in cooperation with eachother. The present invention is therefore capable of achieving moredesirable effects than the method taught in the document mentionedabove.

As stated above, the present invention successfully avoids collisions orsynchronization of transmission data on a telecommunications networkwithout regard to whether or not the network is wired, and can thereforebe used as a communication protocol implementing efficient datacommunications with adaptability and stability.

The present invention is featured with control over the acquisition ofcommunication timing information, i.e. a phase signal in theillustrative embodiments, so that how the timing information is used forcommunication is not a question. For example, when the transmissionfrequency of a data signal is different between nodes, communication maybe effected without setting time slots, in which case the start of datatransmission will be determined in accordance with transmission timinginformation.

While specific examples of the phase response function R(Δθ_(ij)(t)) areshown and described in the first to fifth embodiments, they are onlyillustrative and may be replaced with any other suitable functions.

In the first to fifth embodiments, the collision ratio ci (t) isreflected by the phase Δθ_(i)(t) as both of a stress response functionvalue and the switching characteristic of a phase response functionR(Δθ_(ij)(t)). Alternatively, the collision ratio ci (t) may bereflected by the phase Δθ_(i)(t) only as the characteristic switching ofa phase response function R(Δθ_(ji)(t)), if desired.

In the fifth embodiment, the number-of-types determiner is capable ofreducing the number of types. The function of reducing the number ofnodes may however be applied to the number-of-types determiner of thefourth embodiment as well in order to allow it to selectively increaseor decrease the number of node types, as the case may be.

The entire disclosure of Japanese patent application No. 2005-024175filed on Jan. 31, 2005, including the specification, claims,accompanying drawings and abstract of the disclosure is incorporatedherein by reference in its entirety.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by theembodiments. It is to be appreciated that those skilled in the art canchange or modify the embodiments without departing from the scope andspirit of the present invention.

1. A communication control apparatus mounted on a network nodeconstituting a telecommunications system, comprising: a node typeinformation transmitter/receiver for receiving node type informationselected by a neighboring node, and transmitting node type informationselected by the network node and node type information of another node;a state variable signal transmitter/receiver for receiving a statevariable signal of the neighboring node reflecting a phaserepresentative of a timing of data transmission from the neighboringnode, and transmitting a state variable signal representative of atiming of data transmission from the network node; a node type selectorfor selecting a node type of the network node in accordance with nodetype information of the other node received via said node typeinformation transmitter/receiver; and a transmission timing calculatoroperative in response to the node type information of the network nodeselected by said node type selector, the node type information of theother node and the state variable signal of the neighboring node forvarying a state of the phase of the network node in accordance with atime evolution rule based on a phase response function and asynchronization alliance function for thereby determining a datatransmission timing of the network node.
 2. The apparatus in accordancewith claim 1, wherein said node type selector comprises: a typeselection probability calculator for determining easiness of selectionof each node type in accordance with an adaptability, which isrepresentative of a degree of overlapping selection indicating whetheror not the network node and the other node are selecting a same nodetype, and calculating a probability of selection of each node on a basisof the easiness of selection determined; a type selection executer forexecuting node type selection in accordance with the selectionprobability of each node calculated by said type selection probabilitycalculator; and a convergence determiner for determining that the nodetype of the network node has converged when a particular node typeselected by said type selection executer continues over a predeterminedinterval.
 3. The apparatus in accordance with claim 1, wherein when saidnode type selector uses node type information for a set of nodes n hops,n being a natural number, apart from the network node, transmits asignal to a node range m hops, m being a natural number greater than n,apart from the network node.
 4. The apparatus in accordance with claim1, wherein the phase response function has a dynamic characteristic thatcauses a phase state of the network node to repulse a phase state of theother node, the synchronization alliance function having a dynamiccharacteristic that causes the phase state of the network node to varyin a direction of synchronization relative to the phase state of theother node, said transmission timing calculator causing, when the nodetype information of the other node is identical with the node typeinformation selected by the network node, the dynamic characteristic ofthe synchronization alliance function to appear, and causing, when thenode type information of the other node is different from the node typeinformation selected by the network node, the dynamic characteristic ofthe phase response function to appear.
 5. The apparatus in accordancewith claim 1, further comprising a number-of-nodes determiner forautonomously determining, in the event of selection of a node type, anumber of node types in response to an output of said node typeselector.
 6. The apparatus in accordance with claim 5, wherein said nodetype selector comprises: a stress value calculator for calculating, uponreceiving from said node type selector an adaptability representative ofa degree of overlapping selection indicating whether or not the networknode and the other node are selecting a same node type, a stress valuerepresentative of a degree of non-adaptability if the adaptability doesnot increase over a predetermined period of time in accordance withtime-serial information of the adaptability; and a node type increasingcircuit for increasing the number of nodes when a cumulative stressvalue, which is a sum of stress values calculated by said stress valuecalculator, increases above a first predetermined threshold value. 7.The apparatus in accordance with claim 5, wherein said number-of-nodesdeterminer comprises: a stress value calculator for calculating, uponreceiving from said node type selector an adaptability representative ofa degree of overlapping selection indicating whether or not the networknode and the other node are selecting a same node type, a stress valuerepresentative of a non-adaptability by adding a predetermined weightingfactor matching with a time to time-serial information of adaptabilitiesappearing within a predetermined period of time; and a node typeincreasing circuit for accumulating, when a predetermined period of timehas elapsed from a time at which the time-serial information ofadaptabilities had a maximum value, stress values calculated by saidstress value calculator, and then increasing the number of node typeswhen a resulting cumulative stress value increases above a firstpredetermined threshold value.
 8. The apparatus in accordance with claim6, wherein said node type determiner further comprises a node typedecreasing circuit for receiving adaptabilities from said node typeselector, and reducing, based on the time-serial information of theadaptabilities, a number of node types if the adaptability has a maximumvalue or a value greater than a second predetermined threshold valueinclusive and if a current number of types is greater than an initialnumber of types.
 9. The apparatus in accordance with claim 7, whereinsaid node type determiner further comprises a node type decreasingcircuit for receiving adaptabilities from said node type selector, andreducing, based on the time-serial information of the adaptabilities, anumber of node types if the adaptability has a maximum value or a valuegreater than a second predetermined threshold value inclusive and if acurrent number of types is greater than an initial number of types. 10.A network node constituting a telecommunications system together withanother node and including a communication control apparatus, whereinsaid apparatus comprises: a node type information transmitter/receiverfor receiving node type information selected by a neighboring node, andtransmitting node type information selected by said network node andnode type information of the other node; a state variable signaltransmitter/receiver for receiving a state variable signal of theneighboring node reflecting a phase representative of a timing of datatransmission from the neighboring node, and transmitting a statevariable signal representative of a timing of data transmission fromsaid network node; a node type selector for selecting a node type of thenetwork node in accordance with node type information of the other nodereceived via said node type information transmitter/receiver; and atransmission timing calculator operative in response to the node typeinformation of said network node selected by said node type selector,the node type information of the other node and the state variablesignal of the neighboring node for varying a state of the phase of thenetwork node in accordance with a time evolution rule based on a phaseresponse function and a synchronization alliance function for therebydetermining a data transmission timing of said network node.
 11. Atelecommunications system comprising a network node including acommunication control apparatus, wherein said apparatus comprises: anode type information transmitter/receiver for receiving node typeinformation selected by a neighboring node, and transmitting node typeinformation selected by the network node and node type information ofanother node; a state variable signal transmitter/receiver for receivinga state variable signal of the neighboring node reflecting a phaserepresentative of a timing of data transmission from the neighboringnode, and transmitting a state variable signal representative of atiming of data transmission from the network node; a node type selectorfor selecting a node type of the network node in accordance with nodetype information of the other node received via said node typeinformation transmitter/receiver; and a transmission timing calculatoroperative in response to the node type information of the network nodeselected by said node type selector, the node type information of theother node and the state variable signal of the neighboring node forvarying a state of the phase of the network node in accordance with atime evolution rule based on a phase response function and asynchronization alliance function for thereby determining a datatransmission timing of the network node.
 12. A communication controlmethod applied to a network node constituting a telecommunicationssystem, comprising the steps of: receiving node type informationselected by a neighboring node; transmitting node type informationselected by an network node and node type information of another node;receiving a state variable signal of the neighboring node reflecting aphase representative of a timing of data transmission from theneighboring node; transmitting a state variable signal representative ofa timing of data transmission from the network node; selecting a nodetype of the network node in accordance with node type information of theother node received in said step of receiving the node type information;and determining a data transmission timing of the network node byvarying, based on the node type information of the network node selectedin said step of selecting the node type, the node type information ofthe other node and the state variable signal of the neighboring node, astate of the phase of the network node in accordance with a timeevolution rule based on a phase response function and a synchronizationalliance function.
 13. The method in accordance with claim 12, whereinsaid step of selecting the node type comprises the substeps of:determining easiness of selection of each node type in accordance withan adaptability, which is representative of a degree of overlappingselection indicating whether or not the network node and the other nodeare selecting a same node type, and calculating a probability ofselection of each node on a basis of the easiness of selectiondetermined; executing node type selection in accordance with theselection probability of each node calculated by said substep ofcalculating the probability of selection; and determining that the nodetype of the network node has converged when a particular node typeselected by said substep of executing the type selection continues overa predetermined interval.
 14. The method in accordance with claim 12,wherein when in said step of selecting the node type node typeinformation for a set of nodes n hops, n being a natural number, apartfrom the network node, is used, a signal is transmitted to a node rangem hops, m being a natural number greater than n, apart from the networknode.
 15. The method in accordance with claim 12, wherein the phaseresponse function has a dynamic characteristic that causes a phase stateof the network node to repulse a phase state of the other node, thesynchronization alliance function having a dynamic characteristic thatcauses the phase state of the network node to vary in a direction ofsynchronization relative to the phase state of the other node, said stepof determining the transmission timing causing, when the node typeinformation of the other node is identical with the node typeinformation selected by the network node, the dynamic characteristic ofthe synchronization alliance function to appear, and causing, when thenode type information of the other node is different from the node typeinformation selected by the network node, the dynamic characteristic ofthe phase response function to appear.
 16. The method in accordance withclaim 12, further comprising the step of autonomously determining, inthe event of selection of a node type, a number of node types inresponse to said step of selecting the node type.
 17. The method inaccordance with claim 16, wherein said step of selecting the node typecomprises the substeps of: calculating, upon receiving from said step ofselecting the node type an adaptability representative of a degree ofoverlapping selection indicating whether or not the network node and theother node are selecting a same node type, a stress value representativeof a degree of non-adaptability if the adaptability does not increaseover a predetermined period of time in accordance with time-serialinformation of the adaptability; and increasing the number of nodes whena cumulative stress value, which is a sum of stress values calculated bysaid substep of calculating the stress value, increases above a firstpredetermined threshold value.
 18. The method in accordance with claim16, wherein said step of autonomously determining comprises the substepsof: calculating, upon receiving from said step of selecting the nodetype an adaptability representative of a degree of overlapping selectionindicating whether or not the network node and the other node areselecting a same node type, a stress value representative of anon-adaptability by adding a predetermined weighting factor matchingwith a time to time-serial information of adaptabilities appearingwithin a predetermined period of time; and accumulating, when apredetermined period of time has elapsed from a time at which thetime-serial information of adaptabilities had a maximum value, stressvalues calculated by said substep of calculating the stress value, andthen increasing the number of node types when a resulting cumulativestress value increases above a first predetermined threshold value. 19.The method in accordance with claim 17, wherein said step ofautonomously determining further comprises the substep of receivingadaptabilities from said step of selecting the node type, and reducing,based on the time-serial information of the adaptabilities, a number ofnode types if the adaptability has a maximum value or a value greaterthan a second predetermined threshold value inclusive and if a currentnumber of types is greater than an initial number of types.
 20. Themethod in accordance with claim 18, wherein said step of autonomouslydetermining further comprises the substep of receiving adaptabilitiesfrom said step of selecting the node type, and reducing, based on thetime-serial information of the adaptabilities, a number of node types ifthe adaptability has a maximum value or a value greater than a secondpredetermined threshold value inclusive and if a current number of typesis greater than an initial number of types.